Our work seeks to understand the controls that regulate assembly and organization of the mitotic spindle and cilia assembly. Both of these processes are governed by the centrosome, an organelle that remains largely enigmatic. We are particularly interested in elucidating the molecular mechanisms that govern the switch between centriolar and basal body function, as the assembly of cilia from basal bodies is vital for a large number of developmental decisions. Many human birth defects, developmental abnormalities, and ciliopathies result from defective ciliogenesis or mutations in ciliary proteins. Recently, we have identified and characterized a centrosomal protein, CP110, and a cadre of associated proteins that play important roles in centrosome duplication, assembly of the mitotic spindle, and ciliogenesis. Ultimately, we hope to understand how this network of proteins regulates primary cilia assembly and function and how this process is disturbed in human developmental diseases. Recently, we identified several novel proteins that interact with CP110 and Cep97, including Talpid3 and WDR35, and we have begun to characterize the role of each protein in the context of cilia assembly. Mutations in Talpid3 and WDR35 give rise to developmental defects in diverse animal models, and mutations in WDR35 give rise to birth defects in humans. However, the mechanisms underlying the function of these proteins are not known. Our studies indicate that both proteins are involved in cilia assembly and function. Our proposal is based on three aims that use a combination of biochemistry, proteomics, cell biology, and RNAi. First, we will investigate the function of Talpid3 and WDR35 and ask how these proteins interact with the CP110 complex and how they direct cilia assembly. Next, we will ask how defects in these proteins lead to ciliary defects. We will investigate whether Talpid3 and WDR35 play roles in protein transport between vesicles and basal bodies/cilia and whether they regulate cell growth and quiescence. Third, we will perform biochemical screens to identify proteins that interact with Talpid3 and WDR35. In addition to explaining basic biochemical details regarding the role of CP110-associated proteins, trafficking of proteins into and out of the cilium, and ciliogenesis-processes that remain poorly understood--we will begin to understand the mechanisms underlying human ciliopathies and birth defects resulting from mutations in ciliary disease genes and the phenotypes associated with these diseases.